Substantial use of drugs such as antibiotics can cause several side effects after their absorption into the blood stream; one of them is bacterial resistance. So, it is highly desirable to develop methods of local administration of antibiotics. Such administration makes it possible to apply higher concentration of drug in the target tissue and the influence of systematic administration significantly decreases. The field of nanotechnology in this respect offers a promising approach to develop nanostructured materials for biomedical applications [De, M.; Ghosh, P. S.; Rotello, V. M. Adv. Mater. 2008, 20, 1-17]. These systems present advantages over systemic administration, such as a considerably increased and sustained drug concentration in the crevicular fluid, as well as a reduction of other undesirable side effects associated with systemic drug delivery devices [Rams, T. E.; Slots, J. Periodontology 2000, 1996, 10, 139-159]. Also, the major drawback associated with many of therapeutics is their poor bioavailability and toxicity [(a) Yih, T. C.; Al-Fandi, M.; J. Cell. Biochem. 2006, 97, 1184; (b) Panyam, J.; Labhasetwar, V. Adv. Drug Delivery Rev. 2003, 55, 329]. Therefore, encapsulation of such therapeutics in a pH tunable soluble capsules can provide a novel means of transportation to specific cells or tissues [Schmidt, H. T.; Kroczynski, M.; Maddox, J.; Chen, Y.; Josephs, R.; Ostafin, A. E. J. Microencapsulation 2006, 23, 769].
Tetracycline is one of the most potent broad spectrum therapeutic molecules, which is used extensively to treat bacterial infections associated with bone diseases. It is effective against both gram-positive and gram-negative microorganisms. Local administration of tetracycline is recognized to increase bone regeneration in periodontal defects due to its anti-collagenolytic effect. It also promotes the growth of alveolar bone in periodontal therapy [Park. Y. J.; Lee, Y. M.; Park, S. N.; Lee, J. Y.; Ku, Y.; Chung, C. P.; Lee, S. J. J Biomed Mater Res, 2000, 51, 391]. Therefore controlled delivery of tetracycline may be highly beneficial for the treatment of infectious bone diseases. Various matrices for encapsulation and controlled release of tetracycline includes poly(L-lactide) fibers, PLGA films [Webber, W. L.; Lago, F.; Thanos, c.; Mathiowitz, E. J. Biomed. Mater. Res. 1998, 41, 18] and chitosan microspheres [Bittner, B.; Mäder, K.; Kroll, C.; Borchert, H.-H.; Kissel, T. J. Controlled Release 1999, 59, 23]. Although poly(methyl methacrylate) beads are widely used for treatments, its removal after exhaustion of the antibiotic activity has been a major drawback [Kanellakopoulou, K.; Giamarellos-Bourboulis, E. J. Drugs 2000, 59, 1223].
The drawbacks of the processes are that the methodology is generally tedious sometimes requiring harsh reaction conditions such as extreme pH and higher temperature, organic solvents, emulsion methods, and post-treatments to encapsulate the drug, which may affect the drug stability and efficacy.
CaCO3 when compared to other inorganic materials is ideal as drug delivery system for much therapeutics because of its pH tunable solubility, biocompatibility and biodegradability. As a biomineral CaCO3 is bioresorbable and insoluble at physiological pH but soluble under acidic conditions. The pH around many of the tumors and endolysosomes is acidic [(a) Tycko, B.; Maxfield, F. R. Cell 1982, 28, 643-651; (b) Stubbs, M.; McSheehy, P. M.; Griffiths, J. R.; Bashford, C. L. Mol. Med. Today 2000, 6, 15-19]. Therefore, CaCO3 can be used as a pH-dependent vehicle to deliver the therapeutics through the blood stream to target tissue.
Ideally, the methodology to prepare the host matrix CaCO3 should allow the drug encapsulation during the synthesis of the inorganic host thereby avoiding the post-treatments generally required for inserting the drugs into various matrices. Herein we demonstrate such a facile one-pot synthesis of CaCO3 microstructures under very mild conditions of ambient temperature and pressure, aqueous medium and near neutral pH. The methodology utilizes the self assembly property of polyanions in presence of suitable counter ions to mineralize CaCO3 structures while simultaneously facilitating the entrapment of tetracycline in situ.
It is known that carboxyl groups of biomicromolecules play a crucial role in polymorph stabilization of CaCO3. The carboxylate groups of anionic residues interact with Ca2+ due to charge matching and induce nucleation [(a) Kriwet, B.; Kissel, T. Int. J. Pharm. 1996, 127, 135-145; (b) Euliss, L. E.; Bartl, M. H.; Stucky, G. D. J. Cryst. Growth, 2006, 286, 424; (c) Sonnenberg, L.; Luo, Y.; Schlaad, H.; Seitz, M.; Cö lfen, H.; Gaub, H. E. J. Am. Chem. Soc. 2007, 129, 15364].
Here in present application, the approach is to use anionic polypeptides to interact ionically with cationic peptide oligomers to form assembled structures, which effectively can act as a mold and thereby, dictate the morphology of the mineralized CaCO3. Such phenomena of macromolecular assemblies have been known in the literature [McKenna, B. J.; Birkedal, H.; Bartl, M. H.; Deming, T. J.; Stucky, G. D. Angew. Chem. Int. Ed., 2004, 43, 5652-5655]. However utilization of these assembled structures to minerailize CaCO3 microstructures is the new and nonobvious invention of this patent work. It is shown here that these mineralizing agents aid in controlled crystallization of CaCO3 and can stabilize amorphous and vaterite phases, the thermodynamically less stable polymorphs of CaCO3. More importantly, the methodology allows guest molecules like drugs to be loaded into these microstructures during the preparation.